In theory it's pretty great, in practice, with metered connections you're using up the users internet quota and causing a lot of frustration.
I am used to unmetered internet connections, and after moving to the UK I've spent a lot of time investigating why I'm getting an insane amount of packet loss. I'm talking 30% on weekend evenings.
Long story short, a flatmate was uploading data all day without noticing, the ISP's traffic management kicked in, limited our bandwidth, buffers aren't infinite so packets get dropped [1].
As someone said in a similar thread, this may be the reason for ISPs to drop traffic metering and upload quotas, but I somehow doubt this'll happen.
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1: I've fixed it by limiting the upload quota and bandwidth on my OpenWRT router for that user. I guess I'll have to enable this rule for all other Windows 10 users in my house now.
Not sure if MSFT does this for Comcast but my Windows 10 machine detected the internet connection of 4G dongles (even when it was over normal Ethernet) and prompted me to confirm if it's a metered connection or not.
On a metered connection Windows 10 (as 8.1 before it) is extremely bandwidth conservative it doesn't pull non-critical updates, and other online features such as updating cards, cortana, store function etc. went into austerity mode as well.
But it's highly unlikely that Microsoft can make those guarantees. If this were a robust system, people (especially Microsoft!) would be championing it! But it's clearly not.
In any jurisdiction where you can in practice be held responsible for any data uploaded from your own Internet connection, it's still not OK to upload anything automatically without permission.
This OS is slowly turning into a clusterfuck.